Abstract 4358: Analysis of the cell surface proteome for the identification of candidate diagnostic and therapeutic targets in drug resistant childhood acute lymphoblastic leukemia (ALL)

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Relapse of acute lymphoblastic leukemia (ALL) is a leading cause of cancer-related childhood mortality. Persistence of significant levels of minimal residual disease after almost 6 months of treatment identifies a group of patients with very high risk of relapse (VHR-ALL). Prognostic markers are not available to identify this subgroup at diagnosis. These VHR-ALL patients would qualify for new experimental approaches as part of their initial therapy. Here we present an extensive analysis of the cell surface glycoproteome of ALL cells from 8 VHR-ALL patients and from a corresponding set of ALL patients with good clinical outcome. Given the very limited amount of primary diagnostic material available for research, we have amplified primary human ALL cells in our established xenotransplantation model, using immunodeficient NSG mice. This amplification of primary human material allowed us for the first time to generate normally rare human leukemic cells in numbers sufficient for proteomic studies. We have optimized and extended the mass spectrometry-based Cell Surface Capturing (CSC) technology with complementary enrichment strategies, to increase the protein sequence coverage. Roughly 2500 candidate cell surface proteins were identified. 40% of the candidates were predicted by the TMHMM algorithm to contain a transmembrane domain or a GPI-anchor, also including 174 known CD markers. The immunophenotype analysis of leukemia associated surface markers by flow cytometry at diagnosis was recapitulated in our proteomic dataset in all cases. A semi-quantitative spectral counting approach identified a subset of 200 proteins consistently expressed on most ALL samples and a subset of 60 proteins preferentially detected on the surface of VHR-ALL samples. A subgroup of VHR-ALL, which represented 50% of the analysed cases, was characterized by high expression of members of the vanin (VNN) protein family. Flow cytometry data of VNN-2 from xenografted samples correlated with the semiquantitative estimation of protein levels by the CSC technology. In an independent cohort of 20 ALL samples, we did not detect VNN-2 expression on ALL cells from standard risk patients, while we detected VNN-2 expression in 4 out of 8 cases of high risk or relapsed patients. Anti-VNN-2 antibodies stained the ALL cells homogeneously, indicating that VNN-2 expression could mark the entire population of leukemia cells. Since vanin family proteins have been proposed to mediate interactions between hematopoietic cells and their microenvironment, our findings also provide the basis to evaluate the functional role of vanins in ALL. Our data provide an unprecedented view at the cell surface landscape of the most refractory leukemia cases and identify subsets of cell surface proteins that could be used for diagnosis or therapeutic intervention in this deadly disease. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4358.